It is known that by application of methods of emission and reflectance spectral analysis and evaluation of the state-specific spectral lines as compared with reference standards an analysis of substance mixtures can be carried out. This applies to both the emission spectroscopy by thermal and/or electrical excitation and laser-induced or generally light-induced plasma excitation. Further this applies to the absorption, reflectance and transmission spectroscopy using suitable transmitters in the overall range of electromagnetic radiation. Drawbacks of such spectroanalytical and photometric methods are the fact that in the range of lowest concentration and conformation changes spectral signatures on a very high background are to be detected and that simultaneously the spectral response of the background signal is subjected to strong fluctuations due to ambient and environmental influences. This is for example the case in complex substance mixtures with time-variable or state-variable concentration ratios where frequently the problem arises that one or more lead components of lower concentration are to be detected in the presence of higher-concentration matrix or background components. When the change to be detected in a lead component is equal to or smaller than the statistical or systematical fluctuation of the multi-component mixture or substantial background signals, the application of spectrally high-resolution methods is problematic since in the available detectors, where the spectral bandwidth is narrowed, the interference-signal-to-useful-signal ratio increases. So far this problem has led to failure of spectroanalytical and photometrical methods for detecting small relative concentration changes.